Since the advent of lithium accumulators, the pressing problem of their use has arisen. For example, when used on electric transport with high capacities and currents, such accumulators proved to be very sensitive to overcharge and overdischarge, which causes their breakdown. Accumulators are also sensitive to incorrect operation (memory effect, battery polarity reversal, sulphation, etc.); however, with low capacities and relatively low price, this problem is not that important. The Accumulator Battery Management System (ABMS) solves the task of maintaining the accumulator battery in an optimum condition over a long period of time without the need of frequent intervention of specialists for periodic maintenance and diagnostics. The ABMS also solves a number of secondary tasks related both to the maintenance and diagnostics (in case of serious problems) and (in the long-term perspective) to the addition of new functionality such as monitoring the position of a motor vehicle.
During the operation of accumulator batteries (AB) based on the lithium-ion technology, the task arises of maintaining the cells of ABs in a well-balanced condition because the cells, since they come out of the manufacturing premises, have slightly differing characteristics and this difference can aggravate over time. Without regular monitoring of its condition, an AB can break down rather quickly.
When charging an AB, overcharge of battery cells should be prevented because such overcharge, when one cell is overcharged, causes the charger to stop the process and other batteries could remain not fully charged.
This task has been conventionally solved using special devices called the Battery Management System (BMS) that perform the following functions:                prevention of overcharge of cells (as soon as voltage at any cell becomes lower than a certain threshold, the BMS will forcibly switch off the load until the battery is not put to the charger again);        prevention of overcharge of cells (as soon as voltage at any cells becomes higher than a certain threshold, the BMS switches off the charger);        balancing of cells (when voltage at any cell becomes higher than a certain threshold, which is below the switch-off threshold of the charger, the BMS starts using the excessive charge from the cell through a special energy-consuming element).        
When the balancing of the cells is provided, it means either voltage or charge of the cells equalizing. There are two methods to perform the balancing:                passive,        active.        
When passive balancing is used, the excessive charge of some cells is spent uselessly through resistors so that other cells could continue charging. Such system is simple but it evolves a lot of heat, requires a long time and works only during the charging process. In case of battery discharge, the passive system can switch out the entire battery only, when the weakest cell gets discharged. Thus, the capacity of the entire battery (in ampere-hours) will be equal to the capacity of the weakest cell.
From the prior art, the integrated circuit BQ77PL900 is known, which provides protection of battery blocks with 5-10 batteries connected in series. The said integrated circuit is a functionally complete device and can be used for operation with a battery pack. Comparing voltage of the cell with the threshold, the integrated circuit, if necessary, switches on the mode of balancing for each of the cells. If voltage of any battery exceeds the set threshold, field transistors are switched on and connect the load resistor in parallel to the battery cell, through which the current bypasses the cell and is charging it. In the meantime, the remaining cells continue charging. If voltage drops down, the field transistor gets closed and the charging can continue. Thus, in the end of charging, equal voltage will be present at all cells.
If the balancing algorithm is applied, which only uses voltage deviation as the criterion, incomplete balancing is possible because of the difference of internal resistance of the batteries, where part of voltage is dropping, then current runs through the accumulator, which, in turn, brings an additional error into the spread of voltage in the charge. The integrated circuit of battery protection cannot determine what causes the imbalance—the different capacity of batteries or the difference of their internal resistances. Therefore, with such passive balancing, there is no guarantee that all batteries will be charged for 100%.
The integrated circuit BQ2084 uses the improved version of balancing, which is also based on the changing of voltage but in order to minimize the effect of the spread of internal resistances, BQ2084 carries out the balancing closer to the end of the charging process, when the value of charging current is not high.
In this technology, the charge Qneed is calculated for each battery required for its full charging, after which the difference between Qneed of all batteries is found. Then the integrated circuit switches on the power keys, which discharge all cells to the level of the least charged cell until the charges are equalized.
Since the difference of internal resistances of the batteries does not influence this method, it can be applied at any time, both during charging and during discharging of the accumulator. The main advantage of this technology is a higher balancing of the batteries as compared with other passive methods.
Active systems of control are classed under two classes: the capacity-type systems (built on capacitors) and induction-type systems (built on throttle) all such systems are characterized by the re-distribution of the charge between the cells and such re-distribution only occurs between the neighboring cells of group of cells. Capacity and induction can accumulate the charge and give it up. This is the principle on which the balancing is built. The accumulative cell (C or L) gets connected to the accumulator and accumulates energy from it, and then it gets connected to the neighboring accumulator and gives up the accumulated energy if the connected accumulator has a lower voltage than the accumulative cell. The balancing is achieved over many cycles of energy transfer between the accumulators and the accumulative cells.
Energy is transferred between two neighboring cells of the accumulative battery. By its energy efficiency, this method exceeds the passive balancing because it performs the transfer of energy from the cell with a higher charge to the cell with a lower charge with minimum losses of energy. This method is preferred in cases when it is required to ensure the maximum time of operation without recharging.
From the prior art of active balancing of batteries, the integrated circuit BQ78PL14 of the company TI is known, which is manufactured by the technology PowerPump, which uses the inductive converter for the transfer of energy. PowerPump is using the n-channel p-channel field transistors and a throttle which is positioned between a pair of batteries. The field transistors and the throttle act as a down converter/up converter. Energy losses are not high during this process and all energy runs from the highly-charged battery to the low-charged battery. Because of high current of balancing, the PowerPump technology is more efficient than the normal passive balancing with dissipation of energy. In case of balancing of a battery pack of a laptop, balancing currents are 25-50 mA. Through selection of the values of components, the efficiency of balancing can be achieved, which is in 12-20 times better than with the passive method with internal keys. Typical values of imbalance (below 5%) can be achieved in one or two cycles.
From the prior art, the charge pumping integrated circuit ICL7660 (MAX1044 or the Russian analog KP1168EΠ1) is known, which uses not an inductive-type but capacity-type accumulator (transformation of voltage on switchable capacitors). This integrated circuit is mainly used for gaining negative voltage equal to its source voltage. However, if negative voltage at the exit is, for whatever reason, higher than the positive source voltage, the integrated circuit will start pumping the charge “to the reverse direction”, taking up from the minus and giving up to the plus, i.e. it continuously tries to equalize these two voltages. This feature is used for the balancing of two accumulator cells. The integrated circuit with high frequency connects the capacitor either to the upper or to the lower accumulator. Consequently, the capacitor will be charging from the more charged accumulator and discharging to the less charged accumulator, each time transferring a portion of the charge. Over time, voltages on accumulators will become equal. This system does almost not dissipate energy; the efficiency of the system can reach 95-98% depending on the voltage on accumulators and output current, which depends on the frequency of change-over and capacitor.
Besides, consumption of the integrated circuit only amounts to some dozens of micro-amperes, i.e. it lies below the level of self-discharge of many accumulators and it will perform the work of equalizing voltages on cells. The pumping current may reach 30-40 mA, however the efficiency drops during this process. The source voltage may be from 1.5 to 10 V and this means that the integrated circuit can balance both conventional AA batteries and lithium accumulators.